The present invention relates to a vessel propeller having demountable blades.
The propulsion required for the movement of marine vessels sailing afloat such as boats, ships and under water such as submarines is provided by propellers. Propellers, in general, consist of a central hub and plurality of blades combined with the hub. The surfaces of the propeller blades are generally helicoidal and the flowing water is caught by the leading edge of the blade and compressed on the helicoidal surface to form a pressure and then it accelerates over the blade and leaves from the trailing edge. The course of the fluid on blade surface, and hence the water compression on blade surface affect the amount of thrust to be obtained.
Propellers are conventionally cast in one piece and produced after being machined. In other words, the blades are integrally produced with the hub. This structure has some disadvantages: For example, blades, in general, are not allowed to overlap for the removal of the propellers from the cast mold, and for the surface machining after molding; and therefore such blades can get slightly higher than surface area ratio 1:1, generally being under value of 1 (e.g. 0.950). Another disadvantage of the known propellers is that in case one of the blades is damaged due to mechanical fatigue, external impacts, or some other reasons, the entire propeller needs to be replaced. Moreover, blades must be provided along hub thickness (i.e. along the axis of the hub) in order to obtain maximum thrust from the blades arranged radially around the hub. Production cost of such a complicated structure is high, since a detailed planning before and during operation is required; moreover, huge benches or machine tracks are needed so as to meet the size of the entire propeller.
U.S. Pat. No. 4,930,987, the entire contents of which is incorporated herein by reference, discloses a propeller with demountable blades. The blades are in fact integrally connected to the hub having a dismountable structure each piece of which is integrated with a blade. The disadvantage of the propeller disclosed in U.S. Pat. No. 4,930,987 is that, when one of the blades is to be replaced, the hub needs to be replaced partially, as well. Thus, this necessity leads to the loss of hub material, apart from blade material.
U.S. Pat. No. 3,764,228, the entire contents of which is incorporated herein by reference, discloses a propeller with replaceable blades. The hub is disintegrated and each blade is integrated to these hub parts. In other words, as in U.S. Pat. No. 4,930,987, when one of the blades is to be replaced, the hub needs to be replaced partially as well.
U.S. Pat. No. 1,122,925, the entire contents of which is incorporated herein by reference, has a similar disadvantage. The blades are integrated into the parts of the hub. Moreover, none of the above mentioned prior art references provides an adequately rigid blade-hub connection. Possible consequences of this disadvantage include increased propeller vibration, occurring unbalanced centrifugal forces, noisy operation of the propeller, leading to reduced propeller efficiency.